NOWRAMP 2002

Marine Life Ecology & Shipwrecks in the Northwestern Hawaiian Islands: Artificial Reef Structures and Marine Animal Utilization
Posted by Marc Hughes, UH Hilo Biology and Marine Science student

Maritime archaeology and marine ecology may initially seem to be very disconnected fields of study. Habitation of marine life on wrecks and their utilization of wreckage serves as a connecting tie between these two disciplines. Communities of marine life associated with wreckage caused by ship disasters offer a unique look at the ecology of organisms associated with an unusual anthropogenic habitat. Observations of marine animals around shipwrecks reveal interesting patterns of ecology and often go unnoticed by biologists that strictly focus on natural reef systems. Similar trophic dynamics and predator evasion techniques that rule the lives of marine animals on natural substrate types are often evident around shipwrecks and their associated wreckage. The three dimensional habitat that is produced by shipwrecks provides a multitude of organisms with refuge, attachment sites, and hunting habitat. The shipwrecks in the Northwestern Hawaiian Islands offer a distinctive look at how marine organisms presently take advantage of temporal, artificial reef structures associated with the misfortune swept upon many sailors throughout history.

The techniques we used to explore the wrecks were dependent upon the depth of the shipwreck. We mostly used snorkel gear at sites that were less than 2 meters deep. At sites exceeding that depth we used Scuba diving apparatus. Two team members of the maritime archaeological team (Dr. Hans Van Tilburg and graduate student Suzanne Finney) would photograph the structure, record measurements and take bearings of the wreck. The third member (myself) would collect algae samples, photograph, and record the types and activities of obvious marine life species inhabiting the areas in close proximity to the wrecks.

Shipwrecks in this area of the Hawaiian archipelago leave behind several different types of wreckage that are utilized by marine organisms. The types of wreckage that were encountered on our examinations of the shipwrecks were large sections of relatively intact hull, scattered shards of metal, and anchors and chains. Shipwrecks that occurred within the last 50 to 70 years left behind relatively large sections of metal hull. Older wrecks, having been made mostly of wood, left behind anchors, chains, integral metal machinery, and copper based fastening pins. Wood from older ships is broken down by both decomposition and physical processes (storm generated swells) and therefore do not contribute significantly to wreckage on a long term basis. Species composition of the fauna seemed dependent upon the size of the cover offered by such pieces of wreckage. Large sections of hull were often utilized by crustaceans, schools of medium sized reef fish, large predatory fish, and even monk seals. Solitary anchors, although sometimes very large, were mostly used by smaller reef fish and mollusks.

A large military landing craft submerged next to Tern Island in the French Frigate Shoals had 5 sleeping whitetip reef sharks Trianodon obesus, resting in a cavity created by the overturned craft. The channel through the reef where the landing craft is located is known to be patrolled by tiger sharks Galeocerdo cuvieri during albatross fledgling season (Wegmann, personal communication). The sandy area prevalent around the landing craft offered no such resting or hiding place for the sharks to take refuge, in the event a hungry tiger shark were to focus its attention on the vulnerable White-tip reef sharks.

Two large anchors were stuck in the reef in the same channel. The protruding posts from these anchors were being used as resting places by boobies. Since thousands of nesting birds are present on the island at any given time, resting areas are at a premium which is evident by the raucous squawking of bickering neighbors.

Five anchors are located near the landing at Laysan island. All five were submerged, and partially buried by sand. An endemic snail is found in high densities either directly on or within a few centimeters of the metal structure. The Hawaiian Turban (Turbo sandwicensis) is a soft bodied snail that lives in a protective shell 6 cm in length. The aperture of opening of the shell is plugged by a protective operculum or round calcareous cover when it is inactive or feels threatened. The colorful operculum is green, brown, orange and white and it is often referred to as a "cat's eye" by shell collectors. The operculum is not always reliable in dissuading hungry predators. Numerous locations in the sand flats belied this fact as broken up shells were strewn across the revealing marine habitat. The shell is well camouflaged by blotches of coralline algae on its apex or tip and it blends in well in the algae covering the anchors. They were found in shaded areas where right angles were created by the fluke arms and the shanks of the anchors. Many intact, old shells and operculums were found buried in the sand below the anchors indicating possible long-term use of the anchors by T. sanwichensis.

A shy reef fish, the fantail filefish (Pervagor spilisoma), was found at 4 out of 5 of the anchors. It is very wary species and would seek refuge in any crevice created by the anchors contact with the substrate when approached and photographed. The anchors seem to provide refuge in a habitat, sand and rubble flats, which would be inhospitable to both T. sandwichensis and P. spilisoma due to the conspicuousness and the high level of predation in these areas.

The S.S. Quartette, a ship which grounded in 1952, left a trail of large metal hull and machinery scraps littered on the inside of the shallow reef at Pearl and Hermes Atoll. Numerous species of wrasses including the blacktail wrasse (Thallasoma ballieui) and terminal lined Coris (Coris ballieui) were seen foraging around the wreckage and swimming under and through the spaces under the metal. Two species of fish congregated in relatively large numbers around the wreck and seemed to use the protective areas under the larger metal pieces for refuge. Both the yellowfin goatfish (Mulloidichthys vanicolensis) and the spotfin squirrelfish (Neoniphon samara) were seen fleeing quickly to protected areas of the wreckage when a patrolling squad of predatory giant trevallies (Carynx ignobilis) made lunging bolts towards the schools of vulnerable reef fish. One of the largest species of hermit crabs that sought refuge in the smaller inaccessible recesses of the wreckage is the white spotted hermit crabs (Dardanus megistos). This crab usually relies on the protection of empty shells from the tritons trumpet (Charonia tritonis) or black-lipped tun (Tonna melanostoma). Instead of a calcareous operculum these hermit crabs use their left claw (cheliped) as a plug to block the opening of the shell. These crustaceans are vulnerable to more pernicious predators and their shells are not invincible. Therefore, by hiding in the hard to get at sections of the metal wreckage they effectively use a "shell within a shell" defense technique.

A sunken submarine rescue vessel, the U.S.S. Macaw, at Midway Atoll was a congregating site for many reef fish and is patrolled by Galapagos sharks (Carcharhinus galapagensis). The bow section of the vessel provides a safe spot for a cleaning station at which several morwongs (Cheilodactylus vittatus) were being picked clean of ectoparasites by Hawaiian cleaner Wrasse (Labroides pthirophagous). A thorough inspection of the shaded areas of the wreck revealed titan scorpionfish (Scorpaenopsis cacopsis) lying in wait for prey that were looking for good hiding spots under the wreckage.

A corsair plane located on Midway atoll, at about 40 meters deep, had Hawaiian squirrelfish (Sargocentron xantherythrum), spotted cardinalfish (Apogon maculiferus), and Japanese angelfish (Centropyga interrupta) seeking cover in holes created by missing skin on the outside of the aircrafts framework. A predatory species of scorpionfish, Rhinopias xenops, was found congregating (7 individuals) on the exterior of the wreck. The scorpionfishs cryptic camouflage and motionless hunting technique produces an effective trap for smaller fish looking for shelter.

Kure Atoll had numerous large sections of intact hull of fishing vessels and one particularly large wreck, the Houei Maru (Van Tillburg, personal communication). Several of these sections were still emergent through the waters surface and were being used by black noddies (Anous minutus) and masked boobies (Sula dactylatra) as perching sites. Two sections of the Houei Maru were found at a great distance from each other, one being just inside the reef and the other much farther inside the lagoon. The section just inside the reef seemed to be used by 3 Hawaiian monk seals (Monachus schauinslandi) as a central base for forays. This could be a significant place for these animals to seek refuge, as it is located quite a distance from the nearest beach where they would normally seek refuge. These animals usually hunt far from shore and predation by sharks is not uncommon as is evident by shark bite wounds and scars on seals found on the beach. The section of the wreck found farther inside the lagoon was found to be inhabited by lizardfish (Synodus sp.) and spotfin squirrelfish. Two 20 cm long lizardfish were buried in soft sediment under a large section of metal that created a dark hiding spot. Lizard fish hunt by darting up from the bottom and snatching smaller reef fish with lightning fast speed (ambush predators). Fish that try to evade predators by entering the wreck would literally swim "out of the pan and into the fire."

It seems that a variety of marine organisms utilize the shipwrecks for several different purposes. Many species of both fish and invertebrates use the wreckage material to evade predators and as a safe resting place. Some species of predators use the shipwrecks as hunting areas either as residents hiding in the wreckage or patrolling predators that use the wrecks as a fish aggregating device (FAD). Symbiotic cleaning organisms (Hawaiian cleaner wrasse) which normally "set up shop" at prominent coral heads or outcroppings may utilize artificial coral heads (ship wreckage) to attract fish looking for cleaning stations to have their ectoparasites removed. Ecological patterns that are evident around shipwrecks seem to imitate natural reef dynamics on a smaller scale. Long term investigations into the intricacies of marine organism interactions at shipwrecks would reveal numerous other ecologically significant activities. Shipwrecks act as natural laboratories in which biologists can study aspects such as succession and species composition changes, trophic webs, and symbiosis. Interdisciplinary cooperation in methods of locating shipwrecks and studying both the flora and fauna at these sites is a completely new idea. Research cruises like NOWRAMP 2002 in the Northwestern Hawaiian Islands is responding to the need for interdisciplinary cooperation in these fields and providing insightful new information about marine biology and maritime archaeology.

References:

Dr. Hans Van Tilburg, Maritime Archaeology and History Team Leader

Alex Wegmann, Field Biologist, U.S. Fish and Wildlife Service